There is considerable commercial interest in simple analytical devices, usually of disposable, one-time use form, intended for extra-laboratory usage to conduct biochemical diagnostic assays. Ideally such devices should be operable in a satisfactory manner by lay persons, but this is not as yet normally the case in practice. Many of the currently available devices in fact involve complex manual procedures, with a common feature of such procedures being a requirement to effect a timed sequence of reagent additions to an analyte.